<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<style>
    * {
        margin: 0;
        padding: 0;
    }

    div {
        margin: 100px auto;
        width: 0;
        height: 0;
        /* background-color: red; */
        border: 30px solid transparent;
        border-left-color: black;
        /* border-top-color: red;
        border-right-color: green;
        border-bottom-color: blue; */
    }
</style>

<body>
    <div>

    </div>
</body>

</html>